Composition for and method of electrodeposition of lead



June 21, A, w GE COMPOSITION FOR AND METHOD OF ELECTRODEPOSITION 0F LEAD Filed Oct. 11, 1943 7 O 5N N O \l o 2 MM m n n G M w 0 l N D x m N A l -T|\M G m A T F m a w M W G A w m w w. w m Fm Om\ n S Z ANODE INVENTOR. ANDREW W. LIGER BY c FIG. I

BATH TEMPERATURE -DEGREES F.

PECIMEN A'Nom:

FIG 2 ATTORNEY Patented June 21, 1949 UNITED STATES PATENT OFFICE COMPOSITION FOR AND METHOD OF ELECTRODEPOSITION OF LEAD Delaware Application Getober 11, 1943, Serial No. 505,824

Claims.

My invention relates to a method and an electrolyte for the electrodeposition of lead. More particularly, it pertains to an alkaline lead plating bath and to a method of depositing lead therefrom.

The electrodeposition of lead has interesting applications for the production of corrosion resistant coatings on other basis metals and also for lead refining. For each of these uses, a dense, adherent, fine-grained lead deposit is desired. Of all the baths proposed in the prior art for the electrodeposition of lead, only two have attained any wide-spread commercial use-the fiuoborate and the fluosilicate.

The fiuosilicate bath is more or less stand rd in electrolytic lead refining, while the fluobcrate bath is usually preferred in plating lead on steel and other metals. A recent development in the art of lead plating, comprising a suliainate bath, is described in United States Patent No. 2,318,592. Although these electrolytes are capable of producing lead deposits that are satisfactory for most purposes, they still leave much to be desired from a commercial viewpoint.

Inasmuch as all three of the above-mentioned solutions are distinctly acid, special handling equipment such as glass-, lead-, or rubber-lined tanks, pumps, and pipes are required. In addition, these acid solutions constitute an industrial hazard to the personnel working with them. The fiuosilicate bath is difilcult to prepare for small-scale plating operations; it is subject to decomposition, forming silica and lead fluoride; and it does not give satisfactory plates directly on steel, but requires an intermediate copper deposit between the steel and the lead. The duoborate bath gives slightly better deposits than does the fluosilicate and is more stable.

Numerous attempts have been made, and are recorded in the prior art, to develop an alkaline lead plating bath which would be relatively noncorrosive toward inexpensive iron and steel platin equipment. The plates obtained from these baths, however, tend to be spongy and non-adherent and the baths lack the necessary stability; therefore, they have failed to attain any widespread commercial use in spite of the desirability of eliminating the 'corrosiveness of the acid baths.

It is, therefore, one object of my invention to provide a method of depositing dense, adherent, fine-grained lead electroplates from an alkaline lead plating bath.

Another object of my invention is to develop a relatively non-corrosive electrolyte suitable for use in the electroplating and electrorefining of lead.

A further object of my invention is to provide a method of depositing dense, adherent, finegrained lead electroplates which permits the use of ordinary steel or cast iron equipment to handle the necessary plating solution.

Still another object of my invention is to provide an alkaline electrolyte for the deposition of lead, which is capable of operation at high anode and cathode efliciencies and at low cell voltages.

Still a further object of my invention is to develop an alkaline lead plating bath that is stable over relatively long periods of use, economical, non-corrosive, and easy to prepare.

Various other objects of my invention will be apparent from the following description.

In the drawing,

Figure 1 is a diagram showing the effect of both agitation and bath temperature on the maximum current density practical for the production of good lead deposits from my alkaline lead electrolyte.

Fig. 2 is a view partly in elevation and partly in section illustrating the shape of the specimen used to compare the throwing power of my alkaline lead bath with the lead plating baths in use in the prior art. In this figure, the reference symbols A, B, C, D, E, F, and G indicate the location of measurements to determine the thickness of the lead deposits.

I have discovered that satisfactory, finegrained, adherent lead electrodeposits can be obtained from an alkaline bath if the lead is present in the form of a suitable complex and ii an addition agent is present to refine the grain of the electrodeposited metal and to increase the adherence of the plate to the basis metal. A distinct advantage of my process is that it is not critical in regard to composition limits of the electrolyte or to operating characteristics.

I have found that lead electrodeposits having the desired characteristics can be obtained from a bath having a composition within the following range:

Grams per liter Lead 30 to 95 Rochelle salts 20 to '75 Sodium hydroxide to 360 Addition agent 0.2 to 1.5

In general, in the absence of a relatively high degree of bath agitation, I prefer to operate at a current density of from 20 to 30 amperes per square foot. However, current densities as low as 5 amperes per square foot may be used, and, as is hereinafter disclosed, much greater current densities, for example 400 to G!) amperes per square foot or even higher, may be preferred for certain applications if sufiicient bath agitation is provided. For most Work I prefer to employ 4 stabilizing the bath. Monocarboxylic acids, such as gluconic acid, or their salts, tend to require the use of a relatively high lead concentration as for example between 60 and 95 grams per liter of bath a bath temperature of between 140 and 190 F. 5 for best results. The use of polycarboxylic acids, However, under certain conditions,v temperatures such as tartaric oricitric, or-the salts thereof, of from 125 F., or'lower, up to pp y appears to have an added advantage in my electhe boiling point of the solution may be used. trolyte in that they seem to increase the speed The lead m y be added in any soluble form-and of solution of the lead; the monocarboxylic acids p f a y in the plumbous state::--:Basic lead'calv: do not 'appearto be effective in this latter respect. bonate is readily Soluble; li argeJPbO, issatl excess of alkali over that required to disfactory but somewhat more difiicultly soluble than solve thelead is desirable. While, for economic the basic lead carbonate. "Commercial White lead reasons, I refer to use odium hydroxide, equivaalso m be used, but his ma erial is n -qu lent amounts of other alkalies, such as potassium so readily soluble as the relatively pure basic lead hydroxide tma'y. b sed. In the case of sodium carbonate. Red lead oxide, PbaO i, is not soluble hydroxide, a concentration of at least approxiin the bath. A concentration of 95 g-1'amS'peP-li er mately -9O'-grams-- per liter of bath is preferable. pr s n s about e pp limi of l d in he As isthe case with the aliphatic hydroXy-carbo bath C s en With ood plating p o ylic acids or the salts thereof, larger additions Amounts greatly in excess of this value tend to may be made withoutefiecting the character of precipitate out when the bath is'allowedtostand the plate; however, Ila-advantages are. gained b 'idle fOl a period" Of time. AS" the lead' content exceedin approximately 360g'ramspb1iter, of the bath is decreased," thetend oy form The concentration and. composition or thea-zltrees athigh currentdensitiesincreases. In-oriti agent a can y over relative 1mmder to obtain satisfactory platesat currentdensh limits. In general, I prefer to use from about'0.2 ties i EXCESS 0f p p nsqllare foot, the to approximately 31.5 gramspe'r' liter of bath of lead concentration should be aboveapprox ma ly an alkaline-stable, organi surface active agent. grams per liter of-bath. 'Thelead-content of s h agents as Du .Pc' t .RI-I556 'ancLDli' )Pont the bath remains constant at-the orisin he TLFtl, both available to" the trade ii-cm. E. I. position,-inasmuch as the--maintenance' lead is du t de Nemours an c m d.. t 1 ppli y the an d wh lv at pp trimethyl ammonium bromide are, applicable to mately-lOO- per cent-efiiciencydur g hath Opemmyimproved alkaline lead plating bath. Trition. 'ethanolamine is also quite effective? Beta'ines, or

od DO'taSSiUlIIIz tartmte (Rochelle Salt), their derivatives, having thegen'e'ral'formula a similar compound, iseffective in maintaining the lead in solution. In place of the tartrate, QR L other salts of aliphatic hydroxy carboxylic acids, 3 such as citrates, malates','gluconates, lactates', and ly l t may b ;used.y vEquivalentam nt of where R1 is selected from the group consisting of the respective: acids, themselves, may be added 40 hydrogen d alkyl d' r l tzyRs, and R4 in place of their salts, provided their neutralizarepresent al yl radicals Which-may Co a n tion effect is ofiset by alkali'additions to: secure s u n ch s" hyd xy r pw lk lineproperireealkali concentrationxxIn thelcaseiof l surface active agentslwhieh 'p i the Rochelle salt, there is sometendency forlead y' pp c O- y h invention! The to precipitate out-of the bath during' idle:.periods maximum length f ea y ad eals' i -ed if less than about-'20 grams or" the 'tartrate iper o y by the s b y of the-res l o p liter of the bath is present. I. Amounts in'excess The data in Tabled? shotv'theefieot l ioduoetlon of this concentration appear torhave no effector! the Chit-racer 0f the p 'hy theiadditioh 'o fso the character of the plate; however, for economic of the agents have found to be pp y reasons, I prefer to add not more than approxialkaline leadbath. These-tests-weraconducted mately grams per liter ,1;h;.- Equivalent by adding the-indicated amountsb?thevarious concentrations of the otheralip-hatio hydroxy oraddition agents to-an'electrolyte of: the-1-ollowing ganic acids may be'usedto aid'inchemically composition:

- -TABLE I Character of plate as afieoted' lag various addition agents-in alkaline ZeadAbath Plating A Time Character of Deposit Minutes Coarsely-crystalline, nomadherent.

Good deposit.

Smooth, lustrous; adherent deposit.

Lustrous, nonsadh erent, some 'treein g. Lustrous; adherent; no trees.

- Gooddeposit.

Smooth, lustrousdeposit, some trees.

Smooth, lustrous deposit, n'o'trees.

Smooth, adherent, slightly; coarser than #2.

Same as #9.

Adherent deposit, 'sliglitly'noarser-thail #2. Bright,"smooth;adherentzdeposit. Smooth, adherent, slight porosity.

Very fine grained, adherent deposit. Same as#15.

Same-as 7: 4

Similar to #1 7, withslight pitting.

\ Same as #19; =butslesspitting;

Basic lead carbonate, 75 g./l.; Sodium hydroxide, 180 g./1.; and Rochell salt, g./l. The resulting baths were operated at a current density of 20 amperes per square foot and at a temperature of from 160 to 165 F. Other compounds, such as N-trimethyl-C-decyl-a-betaine, N-dimethylethyl-C-decyl-a-betaine, N-diethylmethyl-C-decyl-a-betaine, N-trimethyl-C-cetyl-a-betaine, N- diethyllauryl-abetaine, and N-triethyl-C-decyla-betaine, are also effective addition agents for use in connection with my invention. When less than about 0.2 gram of the addition agent is present per liter of the bath, the plates tend to be dark, coarsely crystalline, porous, and nonadherent. When more than about 0.2 gram per liter is present, the resultant plate is finely crystalline, semi-lustrous, and thoroughly adherent. Amounts in excess of approximately 1.5 grams per liter are not economic, and, in some cases, the agent tends to separate from the bath in the form of an emulsion. Although additions in excess of 1.5 grams per liter appear to have little advantage, additions up to the point of separation as an emulsion may be made. In some instances the character of the deposit may be further improved by the addition of small amounts, for example from 0. to 2.0 grams per liter, of a wetting agent, such as Duponol ME a sulfonated lauryl alcohol.

Although the alkaline lead plating bath of my invention may be prepared in any suitable and convenient manner, I have found the following procedure to be adequate: About '75 per cent of the final volume of water is introduced into a suitable container and the required amount of alkali is added in small increments with continuous stirring. This addition tends to cause an increase in temperature. The required amount of aliphatic hydroxy carboxylic acid, or of its salt, is then added to the solution, again with continuous stirring. The requisite amount of lead, as basic lead carbonate or other soluble lead compound, is added in small lots, keeping the temperature of the solution above 180 F. and maintaining continuous agitation. When the lead is all in solution, the bath is cooled, filtered to remove any lead that is oxidized to red lead oxide or other insoluble material, diluted to the proper volume, and the required amount of the addition agent added.

As mentioned hereinbefore, my alkaline lead plating bath can be operated over a rather wide range of current densities and temperatures. As is clearly shown in Figure 1 of the drawing, the maximum current density practical for the production of good plates increases as the temperature of the bath and the amount of bath agitation increase. Under the conditions shown in Figure 1, representing those of relatively quiet bath operation, the maximum current densities permitting the production of good electrodeposits vary from about 5 to amperes per square foot, depending upon the bath temperature. Under conditions of more violent agitation, much higher current densities may be used. Under the latter conditions, current densities of 500 amperes per square foot or higher are entirely practical. The data for Figure 1 were obtained from an electrolyte of the following composition: Basic lead carbonate, g./l.; sodium hydroxide, 180 ./l.; Rochelle salt, 35 g./l.; and Du Pont RI-I556, 0.3 to 0.7 g./l.

Data comparing cell voltage measurements for my hereindisclosed alkaline lead bath with those for two commercial acid baths are given in Table II. Identical anodes and electrical arrangements were used for each test. The commercial baths were operated according to the best available data. Anode area, anode spacing, and cathode area and material were also the same in each run. All plates were made directly on plain, lowcarbon steel. The data recorded in Table II show that the operating tank voltage of my alkaline lead bath is about one-third that of the fluoborate bath and only about one-fourth that of the sulfamate bath. Since the anode and cathode efficiencies of all three baths are close to per cent, the lower cell voltage of my alkaline bath results in a lower power cost per unit weight of lead deposited. As shown by the data in Table III, the desirably low cell voltages are obtained in electrolytes having other compositions Within the scope of my present invention. N1 of the tests recorded in Table III were made using a current density of 20 amperes per square foot.

TABLE II Comparative cell voltage data 21 1.01 20 0. Good Deposit, finely crystalline. 22 l. 00 20 0.110 D0.

FLUOBORATE BATH (2)-TEMPERATURE 75 F.

Good Deposit, finely 23 l. 01 20 0. 34 crystalline. 24 1.00 20 0. 35 Do.

SULI AMATE BATH (ID-TEMPERATURE 75 F.

Good Deposit, finely 25 1. O0 20 0. 48 crystalline. 26 1. 00 20 0. 50 Do.

1 Composition of baths: Gramsper (1) Basic lead carbonate Animal glue 3 Du Pont lead sulfamatc salt Du Pout addition agent #1 9. 72

TABLE III Cell voltage data for other alkaline lead baths 0 ll 'l Test Bath 1 e emper- No. No. Voltage agufir e, Remalks 1 0.12 Smooth, lustrous cleposit. 2 0. 12 150 Slightly coarser than #27. 3 0. 15 162 Similar to #28, some treemg. 4 0. 15 Slightly rough. 5 0.10 163 Very lustrous, few pits. 6 0. 20 100 Slightly rough. b 0. 08 164 Smooth and lustrous.

1 Bath compositions: 50 g./l. basic lead carbonate, g./l. sodium hydroxide, 20 51/1.

lactic acid, 0.2 g./l. Du Pont RH556. 50 g./1. basic lead carbonate, 180 g./l. sodium hydroxide, l0 gill.

lactic acid, 0.2 g./l. Du Pout B11556. 50 g./l. basic lead carbonate, 180 g./l. sodium hydroxide, 60 g./l.

lactic acid, 0.2 g./l. Du Pout RH556. 50 g./l. basic lead carbonate, 180 g./l. sodium hydroxide, 20 g./l.

glucouic acid, 0.6 g./l. Du Pont RH 556. 94 g./l. basic lead carbonate, 360 g./l. SOdlllm hydroxide, 40 g./l.

gluconic acid, 0.6 g./l. Du Pont RH 556. 94 g./l. basic lead carbonate, 360 gJI. sodium hydroxide, 20 g./l.

lactic acid, 0.2 gJl. Du Pont B11556.

Aifurth'er advantage ofmy alkaline lead bath is it's-relatively high throwing power. Compari son tests of throwingpower were made in the 8 that'carbon additionsup to a maximum of at least 55' grams per liter ha-ve'no deleteriouseffects on the depositedm-etal-or onthe bath operation.

TABLETiIV'.

Comparative throwing power data Current Thickness of Lead Depositin Inches at Position 2 Density, Plating Test No. Amps. Nlltlm? per mu es I Sq. It. A B C D E F G ALKALINE LEAD BATH- TEMPERATURE 165 F.

FLUOBORATE' BATH TEMPE'R ATURE 75 F.

35 20 0.00085 0.00085 0200000 Y 0.00000 0.00000 0100060 OI 00135 SULFAMATE 'BATIT- TEMPE'RATURE 75 F.

1 Bath compositions shown in Table II. 2 Position on specimen as indicated by Figure 2.

Table II. In conducting these tests, the specimens were immersed in the respective baths in such a manner that 5 inches of the total length was plated. The specimens were positioned with the long axis of the U parallel to the surface of the bath, and anodes were placed on the extension of the long axis approximately inch from the open and the closed ends of the U. After plating, the thickness of the lead electroplatewas determined at the locations designated by the reference symbols A, B, C, D, E, F, and G of Figure 2. These measurements were made along the central axis of the specimen. The data in Table IV show the results of these tests. By dividing the plate thickness at D by the average plate thickness at A and G and multiplying the result by 100, values for the throwing power of the respective baths may be obtained. On this basis, the throwing power of my alkaline lead bath is indicated to be 14 per cent of the ideal, While the sulfamate and the fiuoborate baths have values of 8.85 per cent and 0.0 per cent of the ideal, respectively. In other words, my alkaline bath is superior in throwing power to either the sulfamate or the fiuoborate baths. In addition, the plates from the alkaline bath showed less tendency to tree on some of the higher current density points.

The alkaline bath of my invention has an excellent operable life. Although the addition agent 1 must be replaced from time to time, the consumption of the agent is quite low. For example, in the case of Du Pont RI-I556, the apparent consumption is approximately 0.01 gram per liter per ampere'hour of use. Inasmuch as a relatively large portion of the loss occurs through mechanical dragout, the true addition agent consumption is actua'llywell under the aboveementioned-fi'gure.

Over relatively long periods of operation; the alkaline bathtends to pick up. carbondi'oxide from the atmosphere, forming alkali cai-"bonate in' -the'bath'. However; actualftests haveishown g In general; the electrodepositsfrom my-alkaline bath have been investigated and compare favorablywith-plates from acidtype baths inreg-ard -to porosity, atmospheric corrosion resistance with and without a copper undercoat, resistance to chemical attack, adherence and solderability.

Itcanube-seen;from-the above that I have developed-a new-andnovel electrolyte-and method for the: electrodeposition,-- electroforming, and

electrorefiningof lead Lead-deposited by means of .my. invention isdense. adherent, and finegrained.- .Theelectrolyte is relatively non-corrosive to iron-and steel equipment-0r to any other materials' -commonly-used -for--alk-aline baths, such as glass, .wood. and certain types of rubber; it operates at lowcell voltages; it is stable overlong periodsof use .and it. has a-relativelyhig-h throw ingpower. Thelead deposits from .the disclosed electrolyte are satisfactory for use" in the-wellknownapplications :of leadplating.

While specific examples have been-given in the foregoingspecificatiom-these examples are given 1 merely to illustrate the principles of my invention; and the invention'is notlimit-edto or by such examples.

I-I'aving v thus; described my invention, what I claimis:

1. An alkalineelectrolyte sui'tab-le'for thedeposition of dense, adherent lead electrodeposits'; said-electrolyte containing from 30- to '95 grams per liter of dissolvedlead, from 20 to --grams per literof a salt of an aliphatic hydroxy car'- box-ylic.a cid,'.alkali equivalent tofromto 360 gramssper liter .of sodium hydroxide," and from O2. to '115.grams..per liter of-a betaine, the balanceof said electrolyte being primarily I water.

2. An alkaline-electrolyte suitable for thedeposition. ofdense; adherent lead 'electrodeposits,

saidl electrolyte containing :from 30 to '95 grams pen-liter. ofdissolvedlead, from 20 to .75 grams per liter-of a salt-of tartaricacid, alkaltequivalent to from.90 to 360 gramsper literof'sodiumhydroxide, and from 0.2 to 1 1.5 grams per; liter" of ab etaine, the-balance. of said electrolytebeing said ,'.electrolyte containing. from '30; to grams,- prilliterl of dissolved lead. from 20 to .75 grams 9 l per liter of a salt of citric acid, alkali equivalent to from 90 to 360 grams per liter of sodium hydroxide, and from 0.2 to 1.5 grams per liter of a betaine, the balance of said electrolyte being primarily water.

4. The method of producing dense, adherent lead electrodeposits which comprises making the article to be plated the cathode in an alkaline electrolyte containing from 30 to 95 grams per liter of dissolved lead, from 20 to 75 grams per liter of a salt of an aliphatic hydroxy carboxylic acid, alkali equivalent to from 90 to 360 grams per liter of sodium hydroxide, and from 0.2 to 1.5 grams per liter of a betaine, the balance of said electrolyte being primarily water, and passing an electric current therethrough of sufficient strength and for a sufiicient time to produce the desired thickness of deposited lead.

5. The process which comprises electrodepositing lead from an aqueous alkaline solution containing alkali metal plumbite in concentration equivalent to about 6 oz./gal. of PhD and about REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,619,835 Summers Mar. 8, 1927 2,048,594 Brockman July 21, 1936 2,107,806 Soderberg et al Feb. 8, 1938 2,255,057 Holt Sept. 9, 1941 OTHER REFERENCES Transactions of the Electrochemical Society, vol. 23, page 175 (1913).

Transactions of the Electrochemical Society, vol. 38, page 121 (1920).

Certificate of Correction Patent No. 2,474,092. June 21, 1949. ANDREW W. LIGER It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 8, line 1, for the Word carbon read carbonate;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 6th day of December, A. D. 1949.

THOMAS F. MURPHY,

Assistant Gommz'ssz'oner of Patents. 

